In this paper we formulate answers to three important questions related to Givetian carbonate records and their use for reconstructing million-year past palaeoenvironmental changes. First, we provide ... [more ▼]

In this paper we formulate answers to three important questions related to Givetian carbonate records and their use for reconstructing million-year past palaeoenvironmental changes. First, we provide detailed illustrations of the fascinating diversity that shaped a significant shallow reefal platform during the early- to late-Givetian in the Rhenohercynian Ocean; secondly we improve the sedimentological model of the extensive Givetian carbonate platform in the Dinant Basin and thirdly we evaluate the application of magnetic susceptibility (MS) as a tool for long-term trend correlations and palaeoenvironmental reconstructions. These goals are reached by making sedimentological, geophysical and geochemical study of the La Thure section. Through the early-late Givetian interval we discerned eighteen microfacies ranging from a homoclinal ramp to a discontinuously rimmed shelf and then a drowning shelf. The comparison of these sedimentological results with those published in the south of the Dinant Syncline allowed us to provide an up to date model of the vertical and lateral environmental development for one of the largest Givetian carbonate platforms in Europe. This comparison also increased the knowledge on the facies belts distribution into the Dinant Basin and allowed us to highlight the Taghanic Event. Palaeo-redox proxies reveal a substantial change in the oxygenation level, from oxygen-depleted to more oxic condition, between middle and late Givetian. We demonstrated the relationship between variation in MS values and proxies for siliciclastic input (such as Si, Al). The La Thure is considered as a key section for the understanding of internal shelf settings bordering Laurussia’s south-eastern margin. [less ▲]

In this study we formulate answers to three important questions related to Givetian carbonate records and their use for reconstructing million-year past palaeoenvironmental changes. First, we provide ... [more ▼]

In this study we formulate answers to three important questions related to Givetian carbonate records and their use for reconstructing million-year past palaeoenvironmental changes. First, we provide detailed illustrations of the fascinating depositional diversity that shaped a shallow reefal platform during the early- to late-Givetian in the Rhenohercynian Ocean; secondly we improve the sedimentological model of the Givetian carbonate platform in the Dinant Basin (Belgium) and thirdly we evaluate the application of magnetic susceptibility (MS) as a tool for long-term trends, correlation, and palaeoenvironmental reconstruction. These three goals are reached by making a detailed sedimentological, geophysical and geochemical study of the La Thure quarry. Petrographic analyses revealed eighteen microfacies which represent a carbonate platform evolution through early-late Givetian time, ranging from a homoclinal ramp to a discontinuously rimmed shelf and then a drowning shelf. These results allowed us to illustrate the fascinating environmental diversity that shaped one the largest carbonate platforms of Europe and provide an up to date model of the vertical and lateral development of the Belgian Givetian platform. Early-late Givetian La Thure sequence reveals five main depositional intervals, which could be correlated with the southern margin of the platform. These correlations allowed us to define the facies belts distribution, the major depositional changes that affected this platform and to highlight the Taghanic Event. Palaeo-redox proxies reveal a significant change in the oxygenation level, from oxygen-depleted to more oxic condition, between middle and late Givetian. This change is well-correlated with an increase in global temperature in the late Mid Devonian. Combination of MS and geochemistry demonstrates the inherent-parallel link existing between variation in MS values and proxies for siliciclastic input (such as Si, Al). Collected geochemical and MS data confirm that the La Thure can be considered as a key section for the internal shelf setting in the Rhenohercynian Ocean bordering Laurussia’s south-eastern margin. [less ▲]

The Silurian (Llandovery) and the Devonian (Frasnian) are a periods of interest because sediments and organic-rich shales were deposited in many places that form important hydrocarbon reservoirs and ... [more ▼]

The Silurian – Devonian succession have been deposited in wide sags and sub-basins in a cratonic setting, along the northwestern passive margin of the Gondwana during the opening of the proto-Tethyan ... [more ▼]

The Silurian – Devonian succession have been deposited in wide sags and sub-basins in a cratonic setting, along the northwestern passive margin of the Gondwana during the opening of the proto-Tethyan ocean. During this Siluro-Devonian Period, a high subsidence occurs stacked sediment bodies and organic-rich shales were deposited in many places that respectively form important hydrocarbon reservoirs and source rocks throughout North Africa basins and Arabia (Boot et al., 1998 ; Lüning et al., 2000), which lead Algeria to hold the fourth position in terms of the estimates of technically recoverable shale oil and shale gas resources, based on major basin assessment in the world (EIA, 2013). In the prolific Illizi and Berkine basins (western Ghadames, Algeria) a basin-wide approach is needed, especially with the new “shale gas and shale oil” frontier in the upcoming years, in order to capture regional trends and re-assessment on organic-rich (‘hot’) shale unites which in smaller-scale industrial studies are overlooked. Berkine Basin covers nearly 102.000 km2. This basin has been a thick sedimentary series of 7000 m corresponding to complex reservoirs but also black shales of the basal Silurian and Frasnian respectively major and secondary source rock systems. Wireline-logs from more than 146 (Berkine – Illizi Basins) Algerian petroleum exploration wells have been studies (Djouder et al., 2012; Djouder et al., 2014), and recently 03 months extensive field study of outcrops of the Siluro-Devonian sediments was carried out at the south margin (SE, Tassili n’Ajjer) of the basin. The following analysis incorporates biostratigraphic, ichnological, sedimentological and high resolution stratigraphic data, which provides a framework evolution from offshore to deltaic deposition for the Silurian then fluvial to normal-marine depositional conditions for the Devonian. A total of 06 short-term, third-order sequences can be identified for the Silurian deposits: (i) 'Hot Shale' Oued Imihrou Formation, organic-rich shales with carbonates nodules (Si-1); (ii) above is the Atafaïtafa Formation 500 to 650 m thick with HCS, gutter casts and Cruziana Ichnofacies (Si-2, Si-3); (iii) then overlaid by coarsening-shallowing-upward units. These sequences (Si-4, Si-5 & Si-6) with Storm-wave dominated and Skolithos Ichnofacies are interpreted to reflect deltaic origin. This delta is the result of a significant sea-level drop during the Upper Silurian (Beuf et al, 1971) but also from the high sedimentation rates prograding northwards (Eschard et al., 2005). Devonian deposit also can be divided into fourth third-order sequences (Dev-1 to 4), by the same previous analysis. The base of the cycle is the Caledonian unconformity linked to a tectonic event which affected most of the Gondwanan margin at the Silurian – Devonian boundary and a major relative sea-level fall (Eschard et al., 2005). Previous sequences defined from Tassili n’Ajjer outcrops are well recognized at the basin-scale (Berkine Basin) and can be correlated in the subsurface of the Illizi – Berkine basins (Djouder et al., 2012). Finally, the full depositional cycle for the Silurian – Devonian is reached and capped by the Frasnian maximum flooding surface, with black shales across North Africa (Algeria, western Libya and southern Tunisia) and which are also developed in many parts of the world (Lüning et al., 2003). [less ▲]

The sedimentary basins of North Africa have been accumulated a thick sedimentary succession of Palaeozoic, especially Siluro – Devonian sediments. These successions have been deposited in wide sags and ... [more ▼]

The transition from the Late Devonian to the Early Carboniferous was marked by tectonic events, environmental change and global oceanic biological turnover that influenced sedimentary regimes. The end ... [more ▼]

The transition from the Late Devonian to the Early Carboniferous was marked by tectonic events, environmental change and global oceanic biological turnover that influenced sedimentary regimes. The end-Devonian faunal extinction event, for example, eliminated most of the reef building taxa, which, coupled with an increasing rate of subsidence in response to the opening of the Paleo–Tethys and a sea-ward shift of carbonate factories during the Lower Carboniferous, led to the formation of extensive carbonate ramp platforms along the Laurasian and Gondwanan margins. This development has already been reported from the western Gondwanan and southern Laurasian margins but not from northern to north-eastern Gondwanan margin yet. We aim to improve the knowledge on the main factors controlling the development and growth of carbonate ramps during the Lower Carboniferous by examining the Alborz basin along the northern margin of Gondwana. The Lower Carboniferous Mobarak Formation records the development of a storm-sensitive pervasive carbonate factory on the southern Paleo-Tethys passive margin following the opening of the Paleo-Tethys Ocean into the Alborz basin along the northern margin of Gondwana. Four outcrops in the central Alborz Mountains were studied: the Jaban, Aroo, Shahmirzad and Labnesar sections. Four events have been described as the principal factors controlling carbonate platform evolution in the Lower Carboniferous: (1) A transgression linked to global temperature rise in the Early Tournaisian (Middle Hastarain) resulted in the formation of thick-bedded argillaceous limestones. This interval is represented by massive beds of dark mudstones–wackestones to packstones that laterally interfinger with finely laminated limestones, and with bed thickness ranging on the centimeter to meter scale. This interval correlates with Lower Tournaisian nodular to argillaceous limestones of the Moravia Basin (Czech Republic), the Rhenish Slate Mountains (Poland) and the Dinant Basin (Belgium). (2) Late Hastarian–Early Ivorian glaciations were identified in Southern Gondwana but had not been evidenced in Northern Gondwana yet. This glaciation regime is recorded through the appearance of inner-ramp channel-form facies in mid– and outer-ramp settings. (3) During Late Ivorian–Early Visean?, a differentiation block faulting regime along the basin’s margin caused uplift of the westernmost parts of the Alborz basin and resulted in a sub-marine collapse in the eastern part of the central basin. This caused vast sub-aerial exposure and brecciation the top of the Mobarak Formation at the Jaban and Aroo sections. The sub-marine collapse was recorded through the occurrence of Zoophycos bearing fine-grained limestones in the top of the Labnesar and Shahmirzad sections. (4) Tectonic activity that coincided with considerable and abrupt sea level falls as an indirect consequence of the Viséan and Serpukhovian glaciations phases. This progressive sea level drop led to the stagnation of the carbonate factory, which is expressed as an erosional surface at the top of the Mobarak Formation. [less ▲]

Devonian and Carboniferous deposits are found in many places around the world. The record of climate change preserved in them is the best (and only) resource of information on the Earth`s climate system ... [more ▼]

Devonian and Carboniferous deposits are found in many places around the world. The record of climate change preserved in them is the best (and only) resource of information on the Earth`s climate system then, at a time, when current and future climatic change is one of society`s greatest challenges. This book introduces some of the key areas of Mid-Palaeozoic sediment occurrence worldwide, authored by 114 specialists from more than 30 countries. The areas were studied as part of the UNESCO/IUGS project on climate change and biodiversity patterns in the mid-Palaeozoic (Devonian and Carboniferous). This large-scale taxonomic, stratigraphic and palaeoecological study of mid-Paleozoic floras and faunas has resulted in 86 contributions and more than 25 artistic reconstructions characterizing the biosphere of the Devonian and Carboniferous. Each contribution describes (in English and the respective national language) the scope of the IGCP project in the respective country, exemplified by representative Devonian/Carboniferous age geological sections and/or regions there. The authors intend to enhance the visibility and the perception of relevance of research on mid-Palaeozoic deposits beyond the Earth Science community. [less ▲]

Recent opening of the La Thure quarry in Western Belgium allowed the collection of new data from a poorly outcropping area of the Belgian Frasnian platform. The studied section covers an interval ... [more ▼]

Recent opening of the La Thure quarry in Western Belgium allowed the collection of new data from a poorly outcropping area of the Belgian Frasnian platform. The studied section covers an interval extending from thefalsiovalis to hassi s.l. Zones. Sedimentological analyses allowed the reconstruction of depositional settings in the northwestern part of the Dinant Synclinorium after the demise of the extended Givetian carbonate platform. Two depositional models are distinguished: (a) siliciclastic drowned platform during the Early Frasnian; and (b) a forereef depositional setting belonging to a rimmed shelf during the Middle Frasnian. Moreover, interpreted depositional settings in the northwestern part of the Dinant Synclinorium allowed to constraint the direction of the main facies belts for the Belgian Frasnian platform. Combination of MS and geochemistry demonstrates the inherent-parallel link existing between variation in MS values and proxy for terrestrial input (such as Si and Al). This observation means that, despite the remagnetization occurring within the Belgian Frasnian lithologies, the main trends in the MS signal from the La Thure section still reflect some syn-sedimentary conditions. The increase in MS and clastic input proxies recorded in distal fore-reef deposit within the punctata Zone are likely to be considered as enhanced by rapid and strong shallowing events recognized in the ‘puncataEvent’ interval. [less ▲]

Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth’s ... [more ▼]

Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth’s system. However, no radiometric ages are contained within the Givetian. Consequently, the absolute ages of the Givetian Stage boundaries, as well as the stage’s duration, remain poorly constrained. As an alternative, the analysis of sedimentary cycles allows for the estimation of the duration of this stage. We examined the high-resolution magnetic susceptibility signals of four Givetian outcrops in the Givet area for a possible astronomical imprint, to fully understand the rates of evolutionary and environmental change. All four sections are firmly correlated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing. The highly stable 405 kyr cycles constrain the duration of the Givetian Stage at 4.35+0.45 Myr, which is in good agreement with the International Chronostratigraphic Chart (5.0 Myr). The studied sections also exhibit an imprint of obliquity, suggesting a climatic teleconnection between low and high latitudes. The corresponding microfacies curves demonstrate similar astronomical imprint, and thereby indicate that the observed 10 5year-scale cyclicity is the result of climatic and environmental change [less ▲]

The Lower Carboniferous Mobarak Formation in the Alborz Basin (northern Iran) was deposited along the northeastern margin of Gondwana in a carbonate ramp setting. This paper focuses on the Tournaisian ... [more ▼]

The Lower Carboniferous Mobarak Formation in the Alborz Basin (northern Iran) was deposited along the northeastern margin of Gondwana in a carbonate ramp setting. This paper focuses on the Tournaisian stratigraphic interval of this formation that crops out at the Jaban section in the southwestern Central Alborz Basin. The following facies associations, representing different ramp palaeoenvironments, have been identified: (1) mudstone–wackestone outer-ramp facies; (2) crinoidal to skeletal grainstone–packstone mid-ramp facies; (3) peloidal to crinoidal grainstone–packstone inner-ramp facies; and (4) coastal facies, which include a variety of microbial laminated to oncoidal grainstones and mudstones with evaporitic pseudomorphs. This ramp profile was affected by frequent storms that were responsible for the formation of several skeletal to non-skeletal shoals in the distal mid-ramp to the most proximal inner-ramp areas. The development of the skeletal to non-skeletal shoals along the sea side of the ramp formed a semi-enclosed lagoon sensitive to the influence of both high tides and storm surges.The magnetic susceptibility (xin) of all the samples was measured and compared with that of the facies from which the sample was taken. There is a clear link between xin and the facies; the average xin values were higher for the distal facies than for the proximal facies. The xin profile of this Lower Carboniferous carbonate sequence reflects stratigraphic variations in response to relative changes in sea level and the input of detrital materials. In the context of the sequence stratigraphic framework, the average xin values for lowstand and transgressive systems tract deposits are higher than for the highstand systems tract deposits. The clear link between xin and facies indicates at least a partly preserved primary xin signal related to the detrital inputs. However, to obtain a better understanding of the nature and origin of the minerals carrying the xin, we performed hysteresis measurements on selected samples. It appears that the xin signal is mainly carried by lowcoercivity ferromagnetic minerals such as magnetite, with a mixture of relatively coarse grains (detrital fraction) and ultra-fine grains (probably formed during diagenesis). [less ▲]